Extend basement walls

Good evening,

I am currently planning the renovation of a house and am facing a problem for which I need a few helpful tips.

It is about the following:
The house has 3 floors and is built into a "slope." Thus, the lower floor is open on one side (towards the garden). On the opposite side, the floor is buried.
The house is not fully basemented. The room that is buried is only enclosed by a wall about 50 cm deep (from the ground slab of the ground floor) and nearly ceiling-high covered with earth. It is a bit difficult to explain; I hope it is somewhat understandable.

Now I would like to convert the buried room into an additional basement room, but I would need to extend the outer walls downward to reach the level of the wall in front of it.

My question is whether this is even possible and, if so, roughly what costs I should expect. I will of course have it done professionally, but before requesting a quote, I want to have a rough idea of what I am getting into. To make it a bit clearer, I have attached the side view of the house. The plan shows that the outer wall is too short.

I would appreciate any advice.
Best regards

You want to excavate the "room" at the bottom left? I don't think that's possible. That is not an exterior wall but a strip foundation. If you excavate it, the whole thing might collapse.

I fear so too. I assume that with a suitable support structure it is possible - but it will probably still remain risky and become quite expensive.

You should definitely consult a structural engineer or architect about this. Besides the structural issues, you will probably also have to consider legal regulations regarding thermal insulation, etc. I don't think that, overall, this can be implemented with a good cost-benefit ratio.

Hello,

I am currently planning the renovation of a house

Have you hired an expert or architect?

My question is whether this is even possible and if so, roughly what costs I should expect.

Everything is possible, it just costs ;)

As the excavation proceeds, it must be supported piece by piece, which in turn makes the removal of the existing soil as well as the installation of concrete for the floor slab and the connection to the existing structure more difficult.

Apart from the fact that you should clarify the expected costs with a professional on site, a structural engineer absolutely must come out to look at and examine the entire undertaking. It might even be necessary to involve a geotechnical engineer.

All in all, the costs are likely to be disproportionate to the benefits.

Best regards from the Rhineland